Superposing graphics, such as an underscore with an alphabetic or numeric character pattern, has been achieved by so-called overstriking. Overstriking is printing or displaying two character graphic symbols in one character graphic space. For example, a lower case "g" pattern can be underscored by overstriking with a horizontal line underneath the descender portion, through the descender portion or by breaking the horizontal line only at the outward facing boundaries of the "g" descender. For typographic quality, it is desired that the underscore be broken at all inward and outward facing boundaries of the descender portion with the break being contoured to the descender portion and separated therefrom in accordance with the weight of the "g" character. While ligatures can be constructed to reach the typographic quality desired, computerized printers and displays, such as cathode ray tube displays, electrophotographic printers and the like, employing rectangular arrays of dot patterns have required manually creating raster patterns for implementing the underscore to be overlaid or superposed over the character graphic. As the terms are used herein for underscore purposes, the character graphic is a dominant or superior graphic while the underscore is a recessive or inferior graphic to be interrupted in a manner contoured to, but spaced from, the superior or dominant graphic by an arbitrarily selected distance. In accordance with the present invention, such graphic superposition is fully automatic, such as can be employed in a programmed digital computer.
Superposition of graphics also has been achieved by creating an occlusion signal in video circuits whereby the inferior image is blanked from the video picture while the image being superposed is placed in the occluded area. U.S. Pat. No. 3,961,133 shows such an occlusion signal wherein each line of the raster pattern has an occlusion signal measured in the time domain to make room for the image being superposed on a larger image on the video screen. Such a system does not provide for arbitrary and selective spacings between the images which are contoured to one of the images. Generation of character graphics, including overlapping, is shown in U.S. Pat. No. 3,984,828. This patent uses a bar or rectangular array approach to create a plurality of numerics, none of which allow contouring with selective spacing between superposed graphics.
Similarly, U.S. Pat. No. 4,317,114 shows superposing one graphic on another using an inhibit or NOT function wherein one image is superposed on the other by blanking out the other image, i.e., similar to the first-mentioned U.S. Pat. No. 3,961,133. Examination of this reference showed no selective spacing of one graphic from another for achieving the typographic quality superposed graphic, as mentioned above. Accordingly, there is needed an automatic means of superposing graphic patterns generators which facilitates the generation of typographic quality superposed graphics of all types, particularly for underscoring, no limitation thereto intended.